feat(editor): Make simple conversion engine compatiable with Plain Zhuyin mode

[kanru]

Fixes #620

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.81%. Comparing base (36af8a4) to head (61e8817). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #624 +/- ## ========================================== + Coverage 89.77% 89.81% +0.04% ========================================== Files 42 42 Lines 8759 8781 +22 ========================================== + Hits 7863 7887 +24 + Misses 896 894 -2 ```

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